The rapid growth of information technology has been the main thrust for many advances in communication system developments such as satellite, wireless/mobile, and personal communications. Systems have been envisioned which will allow the communication from any time and place. In many of these systems the final point of contact is usually a wireless loop where antennas will play a crucial role. This puts a high demand on the antenna performance.
Ensuring efficient system operation requires an increased level of antenna integration into the system design right from the inception stage. The demand for high efficiency, compact size, low profile, and conformal construction is increasing. It is also very desirable for the antenna to be amenable to various arrangements of device integration as well as being capable of accommodating various operational requirements. Presently, these requirements are likely achieved by arrays of antenna candidates, which currently are mostly limited to printed structures. The most popular candidate is a microstrip antenna due to fabrication simplicity, low profile, and ease of integration with many devices. It is widely used for applications requiring frequencies ranging from L-Band to millimeter-waves. However, conventional microstrip antennas are known to suffer from a number of disadvantages such as narrow bandwidth, low efficiencies, and higher loss at millimeter-wave frequencies. Recently, a relatively new approach to building microwave antennas based on the use of a dielectric resonator (DR) as the radiating element has been proposed by S. A. Long, M. McAllister, and L. C. Shen, in a paper entitled `The resonant cylindrical dielectric cavity antenna`, IEEE Trans. Antennas Propagat., Vol. AP-31, pp. 406-412,1983. Dielectric resonators (DRs) have been in use for a long time in microwave circuits mainly as energy storage devices. However, since DR boundaries are not conductors, there exists a `loss` mechanism which forms the basis of their use as radiating elements. DRs have been found to overcome some disadvantages of microstrip antennas. They also possess the attractive features of microstrip patches but offer superior performance, particularly, in terms of bandwidth and radiation efficiency.
Dielectric Resonator Antennas (DRAs) are antennas fabricated entirely from low loss dielectric materials and are typically mounted on ground planes. Their radiation characteristics are a function of the mode of operation excited in the DRA. The mode is generally chosen based upon the operational requirement, however, the mode with the lowest Q is typically chosen. Various shapes of DRAs can also be used, including rectangular, disk, triangular, and cylindrical ring to obtain different radiation patterns suitable for a wide variety of applications. R. K. Mongia, A. Ittipiboon, Y. M. M. Antar, P. Bhartia, and M. Cuhaci, describe such an application in a paper entitled `A half-split cylindrical dielectric resonator antenna using slot coupling`, IEEE Microwave and Guided Wave Letters, Vol. 3, pp. 38-39, 1993. In another paper by A. Ittipiboon, R. K. Mongia, Y. M. M. Antar, P. Bhartia, and M. Cuhaci, entitled `Aperture fed rectangular and triangular dielectric resonators for use as magnetic dipole antennas`, Electron. Lett., Vol. 29, pp. 2001-2002, 1993 and yet another paper relating to DRAs is disclosed by A. Ittipiboon, D. Roscoe, R. Mongia, and M. Cuhaci, and is entitled, `A circularly polarized dielectric guide antenna with a single slot feed`, ibid., pp. 427-430.
Various feeding schemes can also be utilized to excite these modes. DRAs have been designed to produce either linear polarization with low cross-polarization levels or circular polarization with very good axial ratio performance over a broader bandwidth than obtainable from microstrip antennas. The reported performance of DRAs up to this point is impressive, however, in accordance with this invention is still further improved.
It is an object of the invention to provide an antenna with improved coupling efficiency and bandwidth by utilizing a high dielectric material between the ground plane and the DRA.
It is yet a further object of the invention to provide a novel method for increasing the coupling efficiency using a thin high dielectric constant strip.